The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Known internal combustion engines include valve trains that have a roller finger follower that transfers rotary motion of a camshaft and, more specifically, a lobe thereof to actuate an engine valve. Known roller finger followers include a body with a first end engaging a lash adjuster and an opposing end that engages a valve stem. For an overhead cam engine, a roller is positioned between the two ends of the roller finger follower for engaging the lobe of the camshaft. The lobe thereby provides pivotal motion about the valve lash adjuster and creates linear motion of the valve and causing the valve to open and close. The timing of the valve opening and closing is important to maximize fuel efficiency, assure complete combustion, minimize emissions, and maximize engine output. Adjustable valve timing can provide preferred valve dynamics for a various range of engine speeds and thereby creating the benefits described above.
Adjustable valve timing can be achieved by a multiple lobe camshaft acting upon a roller finger follower. A first lobe is for low-valve lift engine operation and a second lobe is for high-valve lift engine operation. The cam lobes may have switchable operation or independent finger followers. There may also be a two step finger follower. The two step finger follower is switchable between a low-lift valve actuation position and a high-lift valve actuation position. The low-lift valve actuation position generally includes a lost motion device for reducing the motion received from the cam lobe through the finger follower to the valve. These devices have torsion springs which can create excessive variation in the installed load and create coil binding thereby causing variation in valve lift. These devices do not allow for a third discrete step allowing for a transition between a low valve lift, a high valve lift, and a no valve lift position or for an infinitely variable lift position.